PHILADELPHIA -- Injured Philadelphia 76ers All-Star center Andrew Bynum said Friday he has suffered a "setback" in his return from a knee injury.

Bynum, acquired by Philadelphia in a four-team trade before the season, has yet to play for the Sixers and spoke before a game against Utah.

He has been recovering from a bone bruise on his right knee, and his return has been pushed back three times since the beginning of training camp. The Sixers were hoping Bynum would be cleared to return to basketball activities by Dec. 10.

That date is now in question because of issues with his left knee. Bynum says he now has swelling and a bone bruise on both knees.

"I had a little bit of a setback," Bynum said. "Just working through some issues with the right knee, I kind of have a mirror thing going on with the left knee. I don't know what's going on. The doctors are saying it's a weakened cartilage state, so we kind of wait, I guess. We can't do anything. I just have to wait for the cartilage to get strong."

Bynum did say he targeted Dec. 10 as a possibility, with one to four weeks of basketball-related activity to follow, pushing his much-anticipated debut to anywhere from mid-to-late December to as late as mid-January.